Electronic oscillator control device



Aug. 6, 1940.

I. WOLFF ELECTRONIC OSCILLATOR CONTROL DEVICE Filed Jan. 29, l938` 2 Sheets-Sheet l HIV?" 3 nventor l. WOLFF ELECTRNIC OSCILLATOR CONTROL DEVICE Aug. 6,l 1940.

Filed Jan. 29, 1958 2 sheets-sheet 2 4r/maf cafffA/r.

3 nventor Patented Aug. 6, 1940 UNITED STATES` PATENT orties ELECTRONIC OSCILLATOR CONTROL DEVICE Irving Wolff, Merchantville, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application January 29, 1938, Serial No. 187,596

3 Claims. (Cl. Z50-$6) n My invention relates to the regulation of the ployedtolmaintain the amplitude of an oscillator frequency and amplitude of an electron discharge at a constant value. oscillator, and more particularly to a constant Referring particularly to Figure 1, an enclosed current device for maintaining the frequency quarter wave antenna is shown at 1. This device 5 and/or amplitude of an electron discharge oscilconsists of a conductive rod 3 approximately a latory constant by controlling the magnetic eld, `quarter wave long, mounted within and attached the filament current, or the electrode potentials. to the grounded base of a hollow cylindrical I am aware of the various methods of obtaining metal case 5. An opening 'l is provided through a constant frequency in which the voltage develwhich radiant energy from the oscillator to be oped across a circuit which is resonant near the controlled may induce a voltage on the quarter 10 desired frequency is used to change the frequency wave antenna 3. While I prefer to obtain the generator in a manner which will tend to stabilize control voltage by radiation from `the oscillator, the frequency. Electron discharge devices such obviously it may be obtained by direct, capacitive, as magnetrons and Barkhausen-Kurz oscillators or inductive coupling. y present new problems in frequency and amplitude The combined inductance of the rod 3 and the 15 control because of the ultra high frequenciesincapacitance of the shield 5 are designed so as to volved and because of their inherent erratic resonate near the frequency which is to be mainoperation. For these reasons, the usual methods tained. It has been discovered that a resonant of control would be relatively ineffective; in addicircuit of this nature has an exceptionally high tion, changes in the resonant frequency of the Q, i. e., high ratio of reactance to resistance, and *lo usual control circuit, due largely to changes of consequently when its resonant frequency bears temperature, have a greater effect at ultra high such a relation to the oscillator frequency that` frequencies than at lower frequencies. said oscillator frequency falls on the slope of the It is an object of my invention, therefore, to resonance curve, a small change in the oscillator provide means for stabilizing the frequency outfrequency results in a large change in voltage 25 put of an electronic oscillator. on the resonantcircuit. In' addition, it has been Another object of my invention is to provide found that it' is possible to design a resonant a biasing potential for the control ofthe operatcircuit of this nature which is inherently stable ing characteristics of an electronic discharge with respect to temperature variations. A coudevice. pling coil 2l is placed within `the outer case 5 30 A further object of my invention is to provide in order to loosely couple the antenna to a therma magnetron oscillator having stable frequency ionic tube Il through a coupling capacitor I3. characteristics. Tube Il consists of a heater 2l, a unipotential It is also an objectof my invention to provide cathode I9, and an anode electrode I'l. The means for compensating `for the inherent instacathode I9 is connected to one terminal of capaci- 85 bility of operation of an electron discharge osciltor i3, to the ungrounded end of a diode load lator resulting from the regenerative effect of resistor 23, and to the control grid 28 of a second electron bombardment on the hot cathode. thermionic tube 25. Tube 25 is preferably a pen- A still further object of my invention is to protode similar to RCA type 57 which contains a con- 40 vide means for automatically controlling the trol grid, ak screen grid, a suppressor grid, an 40 magnetic eld intensity of a magnetron oscillator. anode, a unipotential cathode, and a heater.

My invention will be better understood from A rectified D. C. voltage is developed across the following description when considered in conresistor 23 which is positive with respect to nection with the accompanying drawings. Its ground and which is applied to the control grid.

scope is indicated by the appended claims. It is necessary to provide a somewhat greater 45 Referring to the drawings, positive potential for the cathode 29 in order to Figure 1 is a schematic diagram of one embodioperate the tube at the proper point on its charment of my invention; acteristic. I prefer to use a constant voltage Figure 2 is a schematic diagram of a lmodii'icagaseous regulator tube such as RCA type 874 for tion which controls frequencyindependently of this purpose. The degenerative effect of a series 50 changes in amplitude; resistance in the cathode circuit is thereby elimi- Figures 3 and 4 are diagrams showing operating hated. I have accomplished this by connecting a characteristics of a magnetron oscillator; and limiting resistor 33 in series with regulator tube Figure 5 is a schematic diagram representing a 35 between ground and the positive terminal of a modification of my invention whichlmay be emhigh voltage supply 24. The cathode 29 is then A55 vcuit I'.

connected to the movable arm 25 of a low resistance potentiometer 3l shunted across said regulator tube. The effective grid bias on tube 25 is the difference between the voltage appearing from grid to ground and that appearing from cathode to ground. This bias may be adjusted by means of the variable contact 25. Resistor 33 and potentiometer 3l are of such value that the steadyl current through them from source 25 is large with respect to the cathode current of tube 25. The cathode potential then remains substantially constant when the cathode current changes.

The anode 39 is connected to the positive terminal of the high voltage supply through a plate load resistor 4l and directly to the control grid 35 of tube 43, which is also a type 57 tube. This direct connection places grid 35 at a positive potential with respect to ground, and consequently it is necessary to operate its cathode at a slightly higher positive potential. This is accomplished by means of a tap at a point of suitable potential on a bleeder resistor il connected between the positive potential source and ground. The same bleeder resistor supplies potential for the screen grid i9 and also for the screen grid 5i of tube 25.

The anode 32 of tube i3 is connected directly to grid 53 of a fourth thermionic tube 55, which is preferably a low plate impedance triode, such as RCA type 2A3. The anode 5l of this triode is connected directly to the positive terminal of the potential source. The voltage drop from anode 51 to cathode 59, due to the anode current in tube 55, provides the necessary positive anode potential for this tube. Resistor1 6i, which is connected between grid 53 and cathode 55, provides a connection to the positive potential source for the anode 32 of tube 53, and in addition the voltage drop across 6l, due to the anode current of 43, places grid'li at a suitable negative potential with respect to cathode 59. A connection is made from cathode 59 to the oscillator which is to be controlled.

The constant current characteristic of this device may be utilized in different ways, depending upon the requirements. If a controlled potential is required, a resistor may be connected between cathode 579 and ground, and the operating potential for the oscillator taken from the drop across this resistor. A preferred method is illustrated in Fig. l, in which the grid 63 of a Barkhausen- Kurz oscillator 65 is connected to cathode 59. This type of oscillator is so well known that it is not necessary to show its connections in detail. An antenna 56 provides the radiation through which coupling is effected to antenna i.

It is well known that the frequency of electron discharge oscillators is critically dependent upon various electrode potentials. In a Barirhausen- Kurz oscillator, for example, the frequency increases as a function of the positive grid potential. It is evident, therefore, that the frequency of such an oscillator may be controlled by the device illustrated,

Assume that the system is operating in a stable condition on the high frequency slope of the frequency-amplitude characteristic of resonant cir- Energy from the oscillator 5t is radiated from antenna 56, and picked up by antenna 3. If the frequency becomes slightly higher due to a change in supply voltage, or any other cause, the operations which will tend to return the frequency to the original value can be traced in the following manner: The R. F. Avoltage cntherescnant circuit l decreases; the D. C. potential on grid 28 becomes less positive; the anode current in tube 25 decreases; the potential on anode 39 and grid 3B becomes more positive; the anode current in tube 53 increases; the potential on anode 32 and grid 53 becomes less positive; the anode-cathode impedance of tube 55 increases; and the positive grid voltage on grid 63 decreases, which lowers theV frequency. The system will, therefore, stabilize itself at some point dependent upon the circuit constants, and will tend to maintain the oscillation frequency constant regardless of the variation of other factors entering into its operation. In brief, this embodiment of my invention may be described as a degenerative constant current regulating device operated by the frequency of the generated oscillations.

It is, of course, possible to operate the oscillator on the low frequency slope of the frequency-output characteristic of resonant circuit l, but it is then neecssary to compensate for the consequent phase reversal by adding or deducting one stage of: amplication.

In applying my invention to a magnetron oscillator, reference is made to Fig. 3, which graphically illustrates the frequency and amplitude of a magnetron oscillator as functions of the magnetic field intensity. It may be seen that the amplitude passes through a maximum ai'id the frequency increases as the field intensity is increased. When a magnetron is operated on the` peak of the amplitude-field intensity curve, the frequency can be controlled by small changes in the magnetic eld strength without affecting the amplitude. to control the oscillation amplitude manually, by varying the cathode current, for example, or where it is not desirable to operate the magnetron on the peak of the amplitude-field strength curve, it is necessary to provide means for controlling the frequency independently of changes of amplitude. In Fig. 2 I have shown a modification of my invention which accomplishes thisY While shown in connection with a magnetron oscillator, it is obvious that the principle may also be applied to any electron discharge oscillator.

Referring to Fig. 2, it will be seen that resonant circuit i, rectifier Il, ampliers 25 and 43 and control tube 55, with their associated resistors, are connected, and operate, in a manner identical with that shown in Fig. 1. The Barkhausen- Kurz oscillator has been replaced by a magnetron oscillator 85, whose connections are so well known that it is unnecessary to show them in detail. A magnetic eld is supplied by an electromagnet 82. Two coils 84 of this electromagnet are serially connected between cathode 59 and ground. In addition, a resonant circuit 55 has been added which differs from resonant circuit I only in the fact that it is resonant on the opposite side of the desired frequency. Circuit l is resonant below, and therefore circuit 65 is resonant above, the frequency which is to be maintained. A second rectifier Bl, an additional pentode amplifier 59, and a second triode 'll have been added, i

and connected in the same manner as' the rst group shown in Fig. 1. Since the resonant circuits l and t5 are on opposite'sides of the desired However, where it is desirable frequency, the voltage developed across diode y to control tube 1l. This results in one less phase reversal in the additional circuitthan 'in the original circuit, and consequently the additional circuit is brought into phase with the original and their action in controlling the field current is additive. However, a variation in the amplitude of oscillation is applied in phase to the rectifiers Il and 61, and consequently will appear out of phase in the control tubes 55 and ll. The effect of an amplitude variation is therefore eliminated, and the device may be used to control frequency independently of unintentional or intentional changes of output. A further modification to be noted is the inclusion of a resistor T5 between the anode of tube 43 and the grid of tube 55. This is necessary in rder to reduce the gain of the first system to that of the additional system so that uniform control will be exerted by each.

A third modification of my invention in shown in Fig. 5 which is substantially a constant current control device which prevents changes in amplitude of a generated signal. Referring to Fig. 5, an aperiodic antenna is shown at 11. The voltage developed in this antenna from the oscillator 91 which is to be controlled isimpressed across the diode and cathode electrodes of a tube i9. The rectified D. C. potential which appears across a diode load resistor 8| is applied directly to the grid B3 of a thermionic amplifier pentode 85.' Bias for the cathode 81 is obtained in a manner identical with that used in Figs. l and 2, by means of a regulator tube |09, a limiting resistor |02, and a potentiometer |04. The anode 89 is connected to the grid 9| of a low impedance triode 93 which is connected between the positive terminal of the potentialsource 95 and the element which is to be controlled in the oscillator, indicated by 9T. An increase in the amplitude of oscillation causes grid 83 to become more positive, which makes grid 9| less positive and reduces the voltage available for the oscillator 91, tending to reduce the oscillator amplitude.

My invention is not, of course, limited to the control of the operating potentials or the magnetic field intensity, but may, for example, be used to control filament current as shown in my copending application Serial No. 113,184, filed November 28, 1936. The embodiment shown in Fig. 5 is particularly applicable to the latter purpose.

It is further possible that a combination of the methods indicated in Figs.- 5 and 1 may be desirable to control both the frequency and the amplitude of a magnetron oscillator. If this is done, it is necessary to consider the magnetron characteristic which is illustrated in Fig. 4. It will be seen from Fig. 4 that while the cathode current primarily regulates the output of a magnetron oscillator, it has also a secondary effect on the frequency. It will therefore be necessary to operate the frequency control device illustrated in Fig. 1 on the proper side of the required frequency and choose the proper number of intermediate amplifiers so that the undesired effect of a change of magnetic field intensity on the output, and the resultant secondary effect of a compensating change of cathode emission on the frequency do not interact so as to produce instability. The constants should be adjusted so that an increase in magnetic eld intensity causes an increase in output as well as increased frequency.

Thus, if the magnetic field tends to increase in order to keep the frequency constant, the cathode emission, which therefore decreases in order to maintain the output constant, will also tend to increase the frequency. Since both tend to operate in the same direction on the frequency, stability will be reached that much sooner.

The magnetron characteristics shown in Figs. 3 and 4 Awere determined from actual operating conditions. It was noted, however, that the frequency characteristic may reverse itself under certain conditions. The explanation given here applies only to oscillators actually functioning as indicated in Figures 3 and 4. It will probably be necessary, therefore, to determine the frequency characteristic under each set of operating conditions and determine the control method accordingly.

Although I have shown several specific embodiments of my invention for purposes of illustration, other modifications will be apparent to those skilled in the art. For example, a battery may be substituted for the regulator tube shown in various amplifier cathode circuits. In Fig. 2, I have shown two control triodes 55 and ll connected in series, but these may be replaced by a single tube having two grids. Similarly, while I have shown a bleeder resistor 41 for obtaining various operating voltages, I am aware that proper potentials may be supplied by separate batteries. Nor is my invention limited to the particular types of tubes indicated.` My invention, therefore, is not to be limited except as is necessitated by the` prior art and the appended claims.

I claim:

l. In a frequency regulating device, the combination including a positive grid oscillator, a v

resonant circuit, means coupling said` oscillator to said resonant circuit, a rectifier, means connectingv said rectifier to said resonant circuit, means including said rectifier for obtaining a D. C. potential from said oscillations, a source of energizing currents for said oscillator, a thermionic tube, means including said tube connecting said energizing currents to'said positive grid oscillator, and means connecting said D. C. potential to said thermionic tube whereby a control is exerted on the energizing currents for said oscillator tending to oppose a change in frequency of said oscillator.

2. A device for regulating the frequency of a Barkhausen-Kurz oscillator which consists of resonant means receptive to oscillations from said oscillator, said resonant means being tuned to a frequency near said oscillator frequency, means including a rectifier and load resistor for obtaining a D. C. potential which changes in proportion to changes in the frequency of said oscillator, a source of direct current for` energizing said oscillator, a thermionic tube having cathode,` anode, and. grid electrodes, means including the cathode-anode path of said tube for connecting said oscillator to said energizing current, and means for applying said rectified D. C. potentials to said grid electrode, whereby a control is exerted on said energizing current which tends to oppose a change in the frequency of said oscillations.

3. A device of the character of claim 2 which is further characterized by the use of a D. C. amplifier as the means for applying said rectified potentials to said grid electrode. 

